Plant materials
Six-months-old P. massoniana seedlings with similar size were selected and transplanted into the flowerpots filled with approximate 10 kg the aforementioned substrate soil containing different Ca levels. The transplanted seedlings were cultivated in a greenhouse with normal watering condition. Other cultivation conditions as follows: light/dark regime 15/9 h, temperature 21/27°C (night/day), relative humidity 60-70% and photosynthetically active radiation 210 μmol m-2 s-1. After two months growth, the fresh leaf tissues were collected for the subsequent experimental analysis. Three biological replicates were performed for each treatment group.